1. Field of the Invention
The invention relates to endoscopic scissors. More particularly, the invention relates to an endoscopic scissors having scissor elements and a clevis where the scissor elements are held tightly to each other at their pivot point, but are loosely engaged with the clevis.
2. State of the Art
Endoscopic surgery is widely practiced throughout the world today and its acceptance is growing rapidly. In general, endoscopic surgery involves one or more incisions made by trocars where trocar tubes are left in place so that endoscopic surgical instruments may be inserted through the tubes. A camera, magnifying lens, or other optical instrument is often inserted through one trocar tube, while a scissors, dissector, or other surgical instrument is inserted through another trocar tube for purposes of manipulating and/or cutting the internal organ. Sometimes it is desirable to have several trocar tubes in place at once in order to receive several surgical instruments. In this manner, organs or tissue may be grasped with one surgical instrument, and simultaneously may be cut with another surgical instrument; all under view of the surgeon.
By 1996, it is expected that more than two million additional endosurgeries will be performed per year that, in 1990, were done via open surgery (MedPRO Month, I:12, p. 178). The advantages of endoscopic surgery are clear in that it is less invasive, less traumatic and recovery is typically quicker. As a result, many new instruments and devices for use in endosurgery are introduced every year.
Endoscopic surgical instruments generally include a tube, a push rod which extends through the tube, an actuating means engaging the tube and the push rod for imparting reciprocal axial motion to the push rod, end effector means coupled to the push rod by linkage means, and a clevis coupled to the tube at its proximal end and to the end effector means at its distal end, wherein axial movement of the push rod effects movement of the end effector means in a plane parallel to the longitudinal axis of the push rod. For purposes herein, the "distal end" of a surgical instrument or any part thereof, is the end most distant from the surgeon and closest to the surgical site, while the "proximal end" of the instrument or any part thereof, is the end most proximate the surgeon and farthest from the surgical site.
End effectors for endoscopic surgical instruments take many forms and scissors are common among them. Endoscopic scissors, like all scissors, include a pair of scissor elements (blades) attached to the clevis by a threaded pivot axle. Endoscopic scissors may be single acting or double acting. In a single acting endoscopic scissors, a first scissor element is held stationary relative to the clevis and a second scissor element is rotated about the pivot axle relative to the first scissor element. As one or both of the scissor elements are rotated relative to each other about the axle, a moving point of contact between the cutting edges of the scissor elements effects cutting of an object in its path. In endoscopic scissors, as with any kind of scissors it is important to keep the cutting edges tightly pressed against each other at their moving point of contact. It has been known generally in the art of scissors to hold the cutting edges of the scissor elements tightly together by tightening a threaded pivot axle via a screwing action. With endoscopic scissors, however, tightening the threaded pivot axle has an unwanted side effect. Since the pivot axle on which endoscopic scissors rotate is coupled to the clevis, tightening the axle to press the scissor elements together also presses the arms of the clevis together. This results in large frictional forces being generated between the scissor elements and the clevis, thereby making operation of the endoscopic scissors difficult.